1. Field of the Invention
This invention relates to a radiation image reproducing system for scanning a stimulable phosphor sheet with a stimulating ray to cause the stimulable phosphor sheet carrying radiation image to emit light in the pattern of the radiation image stored therein, reading out the emitted light to obtain an electric image signal, and reproducing a hard copy of the radiation image on a recording medium by use of the obtained electric image signal. More particularly, this invention relates to a radiation image reproducing system for forming reproduced images of a size approximately equal to each other on recording media of a predetermined size.
2. Description of the Prior Art
When certain kinds of phosphors are exposed to such radiation as X-rays, .alpha.-rays, .beta.-rays, .gamma.-rays or ultraviolet rays, they store a part of the energy of the radiation. Then, when the phosphor which has been exposed to the radiation is exposed to a stimulating ray such as visible ray, light is emitted from the phosphor in the pattern of the stored energy of the radiation. A phosphor exhibiting such properties is referred to as a stimulable phosphor.
As disclosed in U.S. Patent Nos. 4,258,264, 4,276,473, 4,346,295, and 4,387,428, and Japanese Unexamined Patent Publication No. 56(1981)-11395, it has been proposed to use the stimulable phosphor for recording a radiation image of the human body for medical diagnosis. Specifically, the stimulable phosphor is first exposed to a radiation to have a radiation image stored therein, and is then scanned with a stimulating ray which causes it to emit light in the pattern of the stored image. The light emitted from the stimulable phosphor upon stimulation thereof is photoelectrically detected and converted to an electric image signal, which is processed as desired to reproduce an image of a quality suitable for viewing and diagnostic purposes. The image finally obtained may be reproduced as a hard copy or on a cathode ray tube (CRT). When this radiation image system is practically used for medical diagnosis in a hospital or the like, the image finally obtained is often reproduced as a hard copy on a recording medium such as a photographic material to facilitate filing of the diagnostic data.
When the radiation image system mentioned above is put into practice for medical diagnosis, stimulable phosphor sheets of various sizes are used according to what portions of the object are to be radiographed and, therefore, hard copies of various sizes are obtained therefrom. However, when the sizes of the hard copies differ from one another, the radiologist must observe the hard copies from various distances according to the sizes thereof to correctly read the radiation image information recorded thereon. This is actually very troublesome for the radiologist. Further, the hard copies having various sizes are very troublesome to file and handle during long storage thereof in a hospital, making the work in the hospital inefficient. Therefore, it is desired that the sizes of the hard copies be approximately the same.
Many experiments conducted by the inventors revealed that even when the size of a hard copy is reduced by decreasing the picture element density of a certain degree, the obtained hard copy does not adversely affect the diagnostic efficiency and accuracy.